After stripping away 200 feet of topsoil, the flood ripped away huge
boulders from the underlying lava rock. These boulders were picked up
and carried in the floods only to be stranded in fields and prairies when
the floodwaters subsided. Some boulders, called glacial erratics, were
rafted on icebergs and transported great distances from their source by
the floods of Glacial Lake Missoula.